Ultrafast Rechargeable Aqueous Zinc‐Ion Batteries Based on Stable Radical Chemistry

Abstract Aqueous zinc‐ion batteries (ZIBs) are a promising candidate for fast‐charging energy‐storage systems due to its attractive ionic conductivity of water‐based electrolyte, high theoretical energy density, and low cost. Current strategies toward high‐rate ZIBs mainly focus on the improvement of ionic or electron conductivity within cathodes. However, enhancing intrinsic electrochemical reaction kinetics of active materials to achieve fast Zn 2+ storage has been greatly omitted. Herein, for the first time, stable radical intermediate generation is demonstrated in a typical organic electrode material (methylene blue [MB]), which effectively decreases the reaction energy barrier and enhances the intrinsic kinetics of MB cathode, enabling ultrafast Zn 2+ storage. Meanwhile, anionic co‐intercalation essentially avoids MB molecules rearranging their configuration and sharing Zn 2+ with adjacent functional groups, thus keeps the structure stable. As a result, Zn–MB batteries exhibit an excellent rate capability up to 500C and ultralong life of 20 000 cycles with a negligible 0.07% capacity decay per cycle at 100C, which is superior to that of most reported aqueous ZIBs batteries. This work provides a novel strategy of stable radical chemistry for ultrafast‐charging aqueous ZIBs, which can be introduced to other appropriate organic materials and multivalent ion battery systems.